In-vehicle power supply system to detect failure for a bi-directional DC-DC converter's conversion circuit

Abstract

An in-vehicle power supply system includes a high-voltage direct-current (DC) power supply, a low-voltage storage battery, a DC-DC converter, and a controller. The DC-DC converter includes a conversion circuit including a high-voltage terminal and a low-voltage terminal, an input switch connected between the high-voltage DC power supply and the high-voltage terminal, and an output switch connected between the low-voltage terminal and the low-voltage storage battery. The controller is configured to, after detecting that a current flowing through the conversion circuit exceeds a predetermined current threshold or that a charge voltage of the low-voltage storage battery exceeds a predetermined voltage threshold, execute a failure determination of the DC-DC converter after instructing the conversion circuit to stop a voltage conversion operation, causing the input switch to switch to the disconnected state, and instructing the output switch to switch to the disconnected state. The controller is configured to, in the failure determination execute a first determination operation including an output short-circuit failure determination, an output open-circuit failure determination, and an input short-circuit failure determination. If determining, in the first determination operation, that the output switch does not have failure, controller is configured to execute a second determination operation of determining whether or not the conversion circuit has failure. If determining, in the second determination operation, that the conversion circuit does not have failure, the controller is configured to execute a third determination operation of determining whether or not the input switch has failure. The in-vehicle power supply device determines the location of failure easily.

The invention claimed is: 
     
       1. An in-vehicle power supply system comprising:
 a high-voltage direct-current (DC) power supply; 
 a low-voltage storage battery; 
 a DC-DC converter including
 an input switch including one terminal and another terminal, the one terminal of the input switch being connected to the high-voltage DC power supply, the input switch being configured to selectively switch between a connected state in which the one terminal of the input switch is connected to the another terminal of the input switch and a disconnected state in which the one terminal of the input switch is disconnected from the another terminal of the input switch, 
 a conversion circuit including a high-voltage terminal and a low-voltage terminal, the high-voltage terminal of the conversion circuit being connected to the another terminal of the input switch, the conversion circuit being configured to perform a bidirectional operation of performing a boosting-up operation of obtaining a voltage of the high-voltage terminal by boosting up a voltage of the low-voltage terminal and a stepping-down operation of obtaining a voltage of the low-voltage terminal by stepping down a voltage of the high-voltage terminal, and 
 an output switch including one terminal and another terminal, the one terminal of the output switch being connected to the low-voltage terminal of the conversion circuit, the another terminal of the output switch being connected to the low-voltage storage battery, the output switch being configured to selectively switch between a connected state in which the one terminal of the output switch is connected to the another terminal of the output switch and a disconnected state in which the one terminal of the output switch is disconnected from the another terminal of the output switch; and 
 
 a controller configured to control the DC-DC converter, wherein 
 the controller is configured to, after detecting that a current flowing through the conversion circuit exceeds a predetermined current threshold or that a charge voltage of the low-voltage storage battery exceeds a predetermined voltage threshold, execute a failure determination of the DC-DC converter after instructing the conversion circuit to stop a voltage conversion operation, causing the input switch to switch to the disconnected state, and instructing the output switch to switch to the disconnected state, 
 the controller is configured to, in the failure determination:
 execute a first determination operation including (1) an output short-circuit failure determination of detecting a first low voltage value of the low-voltage terminal and determining, based on the first low voltage value, whether or not the output switch has failure due to short-circuit, (2) an output open-circuit failure determination of detecting a second low voltage value of the low-voltage terminal while controlling the output switch to cause the output switch to be in the connected state, and determining, based on the second low voltage value, whether or not the output switch has failure, and (3) an input short-circuit failure determination of detecting a first high voltage value of the high-voltage terminal and determining, based on the first high voltage value, whether or not the input switch has failure due to short-circuit; 
 if determining, in the first determination operation, that the output switch does not have failure, execute a second determination operation of detecting a second high voltage value of the high-voltage terminal while instructing the output switch to be in the connected state and instructing the conversion circuit to perform the boosting-up operation, and determining, based on the second high voltage value, whether or not the conversion circuit has failure; and 
 if determining, in the second determination operation, that the conversion circuit does not have failure, execute a third determination operation including an input open-circuit failure determination of detecting a third high voltage value of the high-voltage terminal while instructing the conversion circuit not to perform the boosting-up operation and while instructing the input switch to be in the connected state, and determining, based on the third high voltage value, whether or not the input switch has failure. 
 
 
     
     
       2. The in-vehicle power supply system of  claim 1 , wherein
 the conversion circuit further includes:
 a high-side switch including one terminal and another terminal, the one terminal of the high-side switch being connected to the another terminal of the input switch; 
 a choke coil having one terminal and another terminal, the one terminal of the choke coil being connected to the another terminal of the output switch, the another terminal of the choke coil being connected to the another terminal of the high-side switch at a node; and 
 a low-side switch including one terminal connected to the node and another terminal connected to a ground, and 
 
 the controller is configured to, after executing the first determination operation:
 execute a preliminary determination operation of determining, based on a voltage value of the low-voltage terminal of the conversion circuit while controlling the low-side switch to cause the low-side switch to be disconnected, whether or not the low-side switch has failure due to short-circuit; and 
 execute the second determination operation if determining that the low-side switch does not have failure in the preliminary determination operation. 
 
 
     
     
       3. The in-vehicle power supply system of  claim 2 , wherein the controller is configured not to execute the second determination operation if determining that the low-side switch has failure in the preliminary determination operation. 
     
     
       4. The in-vehicle power supply system of  claim 1 , further comprising:
 a converter diode having a cathode connected to the other terminal of the output switch and an anode connected to ground; and 
 an input capacitor having one terminal and another terminal, the one terminal of the input capacitor being connected to the another terminal of the input switch, the another terminal of the input capacitor being connected to ground, wherein 
 the conversion circuit further includes:
 a high-side switch including one terminal and another terminal, the one terminal of the high-side switch being connected to the another terminal of the input switch; 
 a choke coil having one terminal and another terminal, the one terminal of the choke coil being connected to the another terminal of the output switch, the another terminal of the choke coil being connected to the another terminal of the high-side switch at a node; 
 a low-side switch including one terminal connected to the node and another terminal connected to the ground; and 
 a high-side diode having a cathode connected to the input switch and an anode connected to the node, 
 
 the controller is configured to, in the second determination operation:
 if determining that the output switch does not have failure in the first determination operation, charge the input capacitor such that a voltage of the input capacitor becomes a predetermined value by causing the choke coil, the converter diode, and the output switch to operate as a step-down converter by periodically switching the output switch; and 
 then, detect a fourth high voltage value of the high-voltage terminal while controlling the conversion circuit to boost the voltage of the low-voltage terminal while instructing the output switch to be in the connected state, and determine, based on the fourth high voltage value, whether or not the conversion circuit has failure. 
 
 
     
     
       5. The in-vehicle power supply system of  claim 1 , wherein the controller is configured to perform the output short-circuit failure determination and the input short-circuit failure determination, and then perform the output open-circuit failure determination in the first determination operation. 
     
     
       6. The in-vehicle power supply system of  claim 5 , wherein the controller is configured to perform the input short-circuit failure determination, and then perform the output open-circuit failure determination in the first determination operation.